This time the "feature" is Instant Personalization, a quaint moniker that fuzzes the fact that the sites you visit and interact with might suddenly be broadcast for everyone to see, even if you unselect the box to participate.
The Electronic Frontier Foundation elaborates:
More specifically, these sites "may access any information you have made visible to Everyone ... as well as your publicly available information. This includes your Name, Profile Picture, Gender, Current City, Networks, Friend List, and Pages." On Monday, Facebook announced a transition where a "new type of Facebook Page" will make the "current city, hometown, education and work, and likes and interests sections of your profile" publicly available after you go through the transition tool (or those items will be deleted).By default, the "Allow" checkbox for Instant Personalization is checked on your privacy settings. If you don't want the websites that you or your Facebook friends visit to know your information, you must opt out. Since this process is a bit complicated, we have made a quick video showing step by step how to do so.Thankfully, EFF has put together a handy video that helps walk folks through not only opting out of this new feature, but specifically blocking the three applications that are currently participating.
The downside is that there's no easy way to automatically block new sites as they begin to participate, so bookmark the help page demonstrated in the video and check back from time to time in order to manually block additional apps as they come online.